1. Field of the Invention
The invention pertains to a process for producing fibres from an optically anisotropic solution containing cellulose and/or cellulose derivatives, inorganic acids of phosphorus, and water by extruding the solution through a non-corroding spinneret and coagulating the resulting extrudates in a coagulant.
2. Description of Related Art
Such a process is known, int. al., from WO 96/06208. As is described in this application, cellulose fibres can be obtained by spinning and coagulating an anisotropic solution of cellulose in a solvent containing phosphoric acid and/or its anhydrides and water. In this application it is stated to be advantageous to employ a non-corroding. spinneret when spinning such a solution, e.g., a spinneret made of an alloy containing gold and platinum. WO 96/06208 discloses various coagulants. WO 97/19207 discloses a process for producing cellulose fibres from an anisotropic solution containing cellulose formate. This application also states that it is advantageous to employ a non-corroding spinneret when spinning the solution, e.g., a spinneret made of an alloy containing gold and platinum. In the process described in said non-prepublished patent-application the extrudates are coagulated in acetone and washed and dried under low tension.
The processes described in the aforesaid patent applications are especially suitable for the production of cellulose fibres having very good mechanical properties. The obtained fibres have a breaking tenacity which is (much) higher than the breaking tenacity of, say, Cordenka.RTM., i.e., a tenacity in excess of 600 mN/tex. For that reason the fibres described are especially suitable for technical use, e.g., as reinforcement material in conveyor belts, V-belts, and car tyres.
A major drawback to the disclosed processes is that in order to obtain fibres having the aforementioned favourable mechanical properties, use is made of organic solvents as coagulant (e.g., acetone). However, the use of such solvents is not very desirable in view of
a) the additional safety measures required to minimise the risk of explosions and/or fire, PA1 b) the personal protection measures required for staff working on or near a spinning machine, PA1 c) the additional steps required to clear the coagulant of impurities.